1. Field of the Invention
The present invention relates to watering devices for birds and in particular to such devices that maintain the water temperature above freezing.
2. Description of the Prior Art
A number of animal watering devices have been used over the years to provide large quantities of drinking water and to prevent that water from freezing. These devices have been designed primarily for use by either large farm animals or by animals bred in large numbers. While the emphasis of previous devices has been on keeping large quantities of water from freezing and has satisfied the needs of farmers and breeders, the devices have not been practical for the average pet owner or bird enthusiast. Small quantities of water, such as used in a garden birdbath, freeze much more readily and quickly making the problem greater.
Many wild birds stay in climates where water freezes during the winter and have a difficult time finding drinking and bathing water. These birds require a constant supply of water.
Previously, bird lovers only had one method for providing drinking water at below freezing temperatures. It was necessary to frequently monitor the birdbath and either break surface ice or add warm water at intervals. This is not convenient since most people's schedules do not provide time for this type of monitoring.
Temperature controlled heating vessels for cooking and other purposes are common. U.S. Pat. No. 3,806,701 describes a ceramic pot suitable for casseroles, cooking baked beans etc. It has outer and inner walls and a heating element secured to the outer surface of the inner wall.
U.S. Pat. No. 3,820,508 describes a device for maintaining water for horses above freezing. An outer container holds insulating material in which low voltage heating elements are disposed. A separate water container is removably placed inside the outer container to receive heat from the heating elements.
U.S. Pat. No. 3,852,566 describes the use of electrical heating compositions having temperature coefficients of resistivity.
U.S. Pat. No. 4,320,721 describes animal watering apparatus having inner and outer walls, insulation between the two walls and electrical heating elements in the insulation.